There have been known nickel-metal hydride (Ni-MH) batteries, lithium ion secondary batteries (LIB), and the like as secondary batteries. Recently, there is a need for small and high-capacity batteries. Accordingly, in some cases, a plurality of units (hereinafter, called unit cells) each functioning as a secondary cell are superposed.
Structures of a cylindrical type and a rectangular type of nickel-metal hydride (Ni-MH) batteries as illustrated in FIGS. 1 and 2 are disclosed on pages 319-320 in Non-Patent Document 1. A cylindrical type battery 1A is completed as a battery by winding a positive electrode 2 and a negative electrode 3 each being thin-plate-shaped to have a predetermined shape in whorl via a separator 4 (the whorl being perceived as superposed unit cells), inserting the whorl into a cylindrical case 5, and performing sealing after an electrolyte is poured therein. A rectangular battery 1B is completed as a battery by layering structures each having a separator 4 between a positive electrode 2 and a negative electrode 3 each being thin-plate-shaped to have a predetermined shape, inserting the structures into a rectangular case 5, and performing sealing after an electrolyte is poured therein.
In Patent Document 1, there is disclosed an internal structure (electrode plate group) of a rectangular lithium ion secondary battery as illustrated in FIG. 3. In the electrode plate group 1C, positive electrode plates 2 and negative electrode plates 3 are alternately inserted to valley grooves of a continuous body of a zigzag-folded separator 4 and flattened by being pressed in a zigzag direction. Such an electrode plate group is inserted into a rectangular external enclosure and sealing is performed after an electrolyte is poured therein to complete a rectangular battery.
Further, recently, all-solid-state secondary cells structured with solid thin films have been researched and developed as being expected to actualize downsized secondary cells. FIG. 4 is a perspective view and a sectional view illustrating a structure of an all-solid-state secondary cell. In FIG. 4, terminal members such as a positive electrode terminal and a negative electrode terminal, mounting members such as an external member and a cover member, and the like are not illustrated. An all-solid-state secondary cell 1D includes a solid layer (hereinafter, called a storage layer) 6 in which internal change occurs during charging and discharging between a negative electrode layer 3 and a positive electrode layer 2. Examples of the all-solid-state secondary cell 1D include a quantum cell described above and an all-solid-state lithium ion secondary cell. In a case of a quantum cell, a layer (called a charging layer as described later) to store (capture) electrons with a charging operation and to release the charged electrons with a discharging operation is arranged between the negative electrode layer 3 and the positive electrode layer 2. The charging layer corresponds to the storage layer 6. In a case of the all-solid-state lithium ion secondary cell, a solid electrolyte layer is arranged between the negative electrode layer 3 and the positive electrode layer 2. The solid electrolyte layer corresponds to the storage layer 6. Here, in a case that the structure illustrated in FIG. 4 is to be layered as a unit cell, it is preferable that a seal 7 is arranged around the storage layer 6 and the like for providing insulation between the negative electrode layer 3 and the positive electrode layer 2 and for protecting the periphery of the storage layer 6. Here, the seal 7 is not an essential structural element.
As is widely known, regarding the all-solid-state secondary cell 1D as well, terminal voltage can be heightened by layering unit cells in series and energy density can be increased by layering unit cells in parallel.
FIG. 5 is a sectional view illustrating an easily-anticipatable secondary battery 1E in which a plurality of unit cells are parallel-connected with each unit cell being the secondary cell 1D. In the secondary battery 1E, each unit cell 1D is sandwiched between the negative electrode terminal plate 8 and the positive electrode terminal plate 9, and further, an insulation layer 10 is arranged between the positive electrode terminal plate 9 of a unit cell and the negative electrode terminal plate 8 of a unit cell at the one-stage upper side therefrom. A plurality of the negative electrode terminal plates 8 are connected by a negative electrode terminal connection portion 8b and a plurality of the positive electrode terminal plates 9 are connected by a positive electrode terminal connection portion 9b. The negative electrode terminal connection portion 8b and the positive electrode terminal connection portion 9b include extension portions 8a, 9a, respectively, for exposing the negative electrode terminal and the positive electrode terminal to the outside of a mounting member (not illustrated). Assuming that the secondary cell 1D has terminal voltage V0 and current capacity I0, and the number (parallel-connected number) of layers of the secondary cells 1D is N, capacity of the secondary battery 1E becomes to N×I0 (e.g., 6I0 if the number of layers is six) while terminal voltage thereof remains at V0.
To actualize a secondary battery having high terminal voltage and large energy density, unit cells are simply required to be arranged in combination of a multilayer in serial connection and a multilayer in parallel connection. Here, for example, owing to that a unit cell 1D sandwiched between the negative electrode terminal plate 8 and the positive electrode terminal plate 9 in FIG. 5 is replaced with a multilayer of a plurality of unit cells in serial connection, it is possible to structure a secondary battery having higher terminal voltage and larger energy density.